Old (and incorrect) idea of what inertia is. It was once believed that once an object started to rise, it would only rise until it ran out of impetus, in which case it would immediately fall straight to the ground.

Unfortunately, this neglected the fact that projectiles travel in a parabolic curve (because of the constant acceleration due to gravity), and so it was disproven by Newton because it was Newton's laws that introduced inertia, an accurate description of projectile motion.

Im"pe*tus (?), n. [L., fr. impetere to rush upon, attack; pref. im- in + petere to fall upon, seek. See Petition.]


A property possessed by a moving body in virtue of its weight and its motion; the force with which any body is driven or impelled; momentum.

Momentum is the technical term, impetus its popular equivalent, yet differing from it as applied commonly to bodies moving or moved suddenly or violently, and indicating the origin and intensity of the motion, rather than its quantity or effectiveness.


Fig.: Impulse; incentive; vigor; force.


3. Gun.

The aititude through which a heavy body must fall to acquire a velocity equal to that with which a ball is discharged from a piece.


© Webster 1913.

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